With regard to a living tissue such as cardiac muscle, it is very important for the diagnosis of the tissue to objectively and quantitatively evaluate its function. For example, much attention has recently been paid to cardiac resynchronization therapy (CRT) for severe heart failure patients, and much importance has been attached to quantitative evaluation with echocardiography for prior determination for application to CRT and treatment effect determination. CRT is a therapy which can improve the dyssynchrony of cardiac wall motion which tends to coexist in severe heart failure patients. Patients (responders) for whom this therapy is effective have shown dramatic symptomatic improvements. On the other hand, the problem is that patients (non responders) with heart failure cases for whom CRT is not effective occupy as much as about 30% of the patients at the year of 2005.
Non responders are heart failure patients who are not suffering from dyssynchrony. In the past, the application of CRT has been determined with criteria of QRS width >130 msec and ejection fraction (EF)≦35% on electrocardiograms. With these criteria, however, even heart failure patients who are not suffering from dyssynchrony, i.e., non responders, are also included.
Under the circumstances, worldwide attempts have begun to be made to extract only dyssynchrony symptoms by quantitative evaluation methods using echocardiography, and there have been proposed various techniques using velocity arrival time imaging, displacement or strain arrival time (peak time or barycentric time) imaging, and the like. Each of these techniques aims at outputting differences in contraction timing among local cardiac muscles as a color image and allowing easy comprehension of the presence/absence of dyssynchrony and regions with abnormal contraction timings. In this case, “peak time differences of temporal changes associated with a cardiac wall motion parameter” such as velocity, displacement, or strain are most commonly used as contraction timing differences.
It is, however, reported in the PROSPECT study (Circulation. 2008; 117:2608-16) result that using an index in an echocardiographic Doppler method such as velocity or displacement, i.e., a peak time difference, cannot significantly distinguish between a responder and a non responder.
On the other hand, a technique for dissynchrony evaluation using barycentric times as well as peak times has also been proposed. That is, the use of a barycentric time has been proposed in consideration of the fact that stable dissynchrony evaluation cannot be performed by using only a peak when even slight noise mixes in near a peak phase of velocity or displacement or cannot be performed when a plurality of peaks exist. However, even when using a barycentric time, like when using the above peak time difference, some restriction is imposed on the detection of dissynchrony (abnormality) effective for the application of CRT. In addition, since a temporal difference in barycentric time between normality and abnormality is generally smaller than that in peak time, it is difficult to distinguish between normality and abnormality.
Therefore, conventional indices associated with dissynchrony cannot significantly distinguish between responders and non responders for CRT.